Buy this. It's like $8 a can but it is all you need to stick them. I used it on my Dredd drop stickers 4 years and 1000 plays ago and they look like the day I put them on still.

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Remove, flatten, spray the back, let dry for 30 seconds, apply carefully and press firmly. If you buy some, practice with something else first. I use that spray for 4 or 5 other things. It is a great product.